Identity columns in the Cluster Edition behave differently from those in non-clustered editions of Adaptive Server. Although the Cluster Edition guarantees that identity values are unique, for performance reasons the values may not monotonically increase.
In a non-clustered Adaptive Server, a set of identity values are burned into memory to reduce disk I/Os as inserts access the next value from memory. In the Cluster Edition, the same size set is burned into memory, but the set is split among the cluster instances. In a two-instance cluster with an identity set size of 250000, the first instance inserts values {1,2,3, and so on}, and the second instance inserts values {125000,125001,125002, and so on}.
The next-identity function reports the next identity value for a table from the instance in which next-identity is executed. For example, next-identity returns 4 for instance 1 and 125003 for instance 2.
The behavior of the identity-burn-max remains the same as for a non-clustered Adaptive Server because the burn size and burn behavior is unchanged in the Cluster Edition.
